Studies in the structure and synthesis of some natural products

Ph.D.Leon H. Zalko

Update on LIPID MAPS classification, nomenclature, and shorthand notation for MS-derived lipid structures

A comprehensive and standardized system to report lipid structures analyzed by mass spectrometry is essentialfor the communication and storage of lipidomics data. Herein, an update on both the LIPID MAPSclassification system and shorthand notation of lipid structures is presented for lipid categories Fatty Acyls(FA), Glycerolipids (GL), Glycerophospholipids (GP), Sphingolipids (SP), and Sterols (ST). With its majorchanges, i.e. annotation of ring double bond equivalents and number of oxygens, the updated shorthandnotation facilitates reporting of newly delineated oxygenated lipid species as well. For standardized reportingin lipidomics, the hierarchical architecture of shorthand notation reflects the diverse structural resolutionpowers provided by mass spectrometric assays. Moreover, shorthand notation is expanded beyond mammalianphyla to lipids from plant and yeast phyla. Finally, annotation of atoms is included for the use of stableisotope-labelled compounds in metabolic labelling experiments or as internal standards

Critical point network for drainage between rough surfaces

In this paper, we present a network method for computing two-phase flows between two rough surfaces with significant contact areas. Low-capillary number drainage is investigated here since one-phase flows have been previously investigated in other contributions. An invasion percolation algorithm is presented for modeling slow displacement of a wetting fluid by a non wetting one between two rough surfaces. Short-correlated Gaussian process is used to model random rough surfaces.The algorithm is based on a network description of the fracture aperture field. The network is constructed from the identification of critical points (saddles and maxima) of the aperture field. The invasion potential is determined from examining drainage process in a flat mini-channel. A direct comparison between numerical prediction and experimental visualizations on an identical geometry has been performed for one realization of an artificial fracture with a moderate fractional contact area of about 0.3. A good agreement is found between predictions and observations

Tunnelling dominates the reactions of hydrogen atoms with unsaturated alcohols and aldehydes in the dense medium

Hydrogen addition and abstraction reactions play an important role as surface reactions in the buildup of complex organic molecules in the dense interstellar medium. Addition reactions allow unsaturated bonds to be fully hydrogenated, while abstraction reactions recreate radicals that may undergo radical-radical recombination reactions. Previous experimental work has indicated that double and triple C--C bonds are easily hydrogenated, but aldehyde -C=O bonds are not. Here, we investigate a total of 29 reactions of the hydrogen atom with propynal, propargyl alcohol, propenal, allyl alcohol, and propanal by means of quantum chemical methods to quantify the reaction rate constants involved. First of all, our results are in good agreement with and can explain the observed experimental findings. The hydrogen addition to the aldehyde group, either on the C or O side, is indeed slow for all molecules considered. Abstraction of the H atom of the aldehyde group, on the other hand, is among the faster reactions. Furthermore, hydrogen addition to C--C double bonds is generally faster than to triple bonds. In both cases, addition on the terminal carbon atom that is not connected to other functional groups is easiest. Finally, we wish to stress that it is not possible to predict rate constants based solely on the type of reaction: the specific functional groups attached to a backbone play a crucial role and can lead to a spread of several orders of magnitude in the rate constant.Comment: Accepted for publication in A&

Making heads or tails of mitochondrial membranes in longevity and aging: a role for comparative studies

Mitochondria play vital roles in metabolic energy transduction, intermediate molecule metabolism, metal ion homeostasis, programmed cell death and regulation of the production of reactive oxygen species. As a result of their broad range of functions, mitochondria have been strongly implicated in aging and longevity. Numerous studies show that aging and decreased lifespan are also associated with high reactive oxygen species production by mitochondria, increased mitochondrial DNA and protein damage, and with changes in the fatty acid composition of mitochondrial membranes. It is possible that the extent of fatty acid unsaturation of the mitochondrial membrane determines susceptibility to lipid oxidative damage and downstream protein and genome toxicity, thereby acting as a determinant of aging and lifespan. Reviewing the vast number of comparative studies on mitochondrial membrane composition, metabolism and lifespan reveals some evidence that lipid unsaturation ratios may correlate with lifespan. However, we caution against simply relating these two traits. They may be correlative but have no functional relation. We discuss an important methodology for body mass and phylogenetic correction in comparative studies

State v. McKean Clerk\u27s Record v. 2 Dckt. 41004

https://digitalcommons.law.uidaho.edu/idaho_supreme_court_record_briefs/6241/thumbnail.jp

Under the carbon spell: diborane's puzzling structure and the emergence of boron chemistry

Tese de mestrado em História e Filosofia das Ciências, apresentada à Universidade de Lisboa, através da Faculdade de Ciências, 2011Nowadays, boron chemistry is one of the most promising fields of chemistry, with pervading and exciting applications to chemical and pharmaceutical industry, to nanotechnology and medicine. However, during their first three decades, the hydrides of boron had no application whatsoever and it was their puzzling structure that sustained all research on them. Since the isolation of the first hydride of boron in 1912 they had been considered one of the most puzzling phenomena in chemistry and they managed to keep their irreducibility until the 1950’s. In the process, they forced bond theory to abandon one of its most fundamental paradigms: the atom-to-atom bond. The present work offers the first systematic historical account of the borane’s route to industrialization since their discovery, with a strong focus on the role played by the structural debate. The analysis is supported by a very thorough and comprehensive study of the technical questions involved in the dispute. The historical investigation of any scientific field/discipline/specialty can be guided by numerous hopefully complementary approaches and plural methodological commitments. However, in any given area, no truly consistent historical account can exist without an initial systematic and comprehensive assessment of the evolution of its technical problems. It is my contention that this starting point should be the basis upon which social, cultural and intellectual approaches can later (or simultaneously) find their unquestionable grounding and utility. Thus, the present work is clearly assumed to provide such a groundbreaking point of departure. The present work proves that the chemistry of the hydrides of boron was an integral and important part of theoretical chemistry in the twentieth century. No diachronic account of the history of chemistry in the twentieth century can ignore the history of the hydrides of boron. The history of these compounds is essential to put into a more inclusive perspective the history of chemical bond. The history of diborane raises the question of how ideas are able to evolve and be appropriated by other participants in new theoretical contexts. Ignoring the history of the hydrides of boron can only lead to a mistaken perception of their own identity. Such is the case with the presently prevailing idea that up until their use outside the academic environment, they had been laboratory curiosities. The present work demonstrates that during their laboratory phase they were rather seen as a pressing theoretical problem and this perception entirely guided all investigations. An interesting historiographic issue raised by the history of the hydrides of boron is the dramatic role played by war in their mutation into industrial and commercial products. Diborane’s history also has important bearings on the debates over the reducibility of chemistry to physics and the true nature of quantum chemistry. It is in complete agreement with the historiographic vision expressed a few years ago by Jed Buchwald and Allan Franklin and in fact it proves its fertility, at least on what concerns relatively recent historical processes.

Development of novel fluorinated high performance polymers and new biomaterials from renewable resources

New type of high performance polymers, hexafluoroisopropylidene (HFIP)-linked benzophenone polymers, have been synthesized by the Ni(0)-catalyzed coupling polymerization of newly designed bis(aryl triflate) and bis(aryl halide) monomers. New synthetic strategy based on Ni(0)-catalyzed copolymerization has also been developed in order to prepare materials with higher molecular weight and optimized thermal and mechanical properties. The unique structural characteristics of these novel polymers make them potentially interesting candidates for gas separation applications, as well as for electrical applications, such as nonvolatile organic memory;Vegetable oils represent one of the most abundant annually renewable resources in the world today. Utilization of these materials as building blocks for the synthesis of new bioplastics has been described. A variety of promising new polymeric materials, ranging from soft rubbers to hard, tough and rigid plastics have been prepared by the cationic copolymerization of vegetable oils and a range of alkenes initiated by boron trifluoride diethyl etherate. The chemical, physical, thermal and mechanical properties of these polymers have been investigated as a function of the resin composition. Vegetable oil and alkene comonomer reactivities have a direct effect on most of the polymers\u27 properties, which can be reasonably predicted by careful choice of both types of the reactants and the catalyst. The resulting polymers possess good thermal and mechanical properties, including good damping and shape memory properties. As such, these new biomaterials appear promising as replacements for a variety of petroleum-based polymers;A [RhCl(C8H8)2]2 is a highly efficient and selective isomerization catalyst for the production of highly conjugated vegetable oils with a high conjugated linoleic acid (CLA) content. These conjugated products are of great importance in the food, paint, coating, and polymer industries. The elucidation of structural isomers formed during the homogeneous rhodium-catalyzed isomerization of several vegetable oils has been described. The correlation between the distribution of the conjugated isomers, reaction kinetics and the mechanism of the reaction has also been investigated. The high efficiency and selectivity of this isomerization method along with the straightforward purification process renders this approach highly promising for the preparation of conjugated oils and CLA